Be. Christensen et al., THE ROLE OF SIDE-CHAINS IN THE CR3-INDUCED GELATION OF XANTHAN AND XYLINAN (ACETAN) VARIANTS(), Carbohydrate polymers, 25(1), 1994, pp. 25-29
The effect of the length and chemical composition of the side-chains i
n comb-like branched polysaccharides on gelation with trivalent metal
ions has been studied using xanthan and xylinan (acetan) with intact a
nd truncated side-chains. Partial or complete removal of the terminal
beta-D-mannose, or removal of up to 22% of the trisaccharide side-chai
ns of xanthan using partial acid hydrolysis, has only small effects on
the Cr3+-induced gelation. In contrast, replacement of beta-D-mannose
by the trisaccharide alpha-L-Rhap-(1 --> 6)-beta-D-Glcp-(1 --> 6)-alp
ha-D-Glcp-(1 --> 4)- to yield the polysaccharide xylinan totally inhib
its the gelation with Cr3+ ions. Removal of the trisaccharide by parti
al acid hydrolysis, which leads to a series of polymers with structure
s converging towards the partially hydrolysed xanthans, restores the g
elling ability with Cr3+ ions. These observations seem to support the
gelation model where Cr3+-glucuronic acid interactions are involved in
the cross-linking of chains. It is further suggested that this intera
ction can be suppressed due to steric hindrance caused by the bulky si
de-chains in xylinan.